Well that's exactly how I feel, if you want to "upgrade" from the hd600 you have to spend a ton more money. I'd also say the hd600/k701 are the drop off point where you can get away using an amp/dac >$200. I guess O2 and Odac works okay with the lcd 2 but you will still be spending an extra $550 more than the hd600s if you get a good deal.
Agreed. I think that explains the longevity of the HD600. From what I've listened to, a true significant upgrade requires a (minimum) $600 to $700 purchase, and higher. Since you can now easily buy brand new 600's at around $320 to $350, that still defines value to me, not to mention wonderful sound across all genres.